A 3MHz-BW 3.6GHz digital fractional-N PLL with sub-gate-delay TDC, phase-interpolation divider, and digital mismatch cancellation

Digital Fractional-N PLLs allows easy cancellation of ΔΣ quantization noise and spurs [1], [2]. However, the actual results depend dramatically on the linearity of the time-to-digital converter (TDC). This paper presents a 3MHz bandwidth fractional-N synthesizer, which combines a 4ps TDC with digital linearization algorithm and a feedback phase interpolator with mismatch cancellation algorithm. In contrast to other TDC linearization approaches [3], this structure allows multiplier-free computations, fast and accurate spur cancellation, as well as digital post-cancellation of phase errors induced by the phase interpolator mismatches, avoiding more complex calibration loops [4].

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[6]  Matthew Z. Straayer,et al.  A Low-Noise, Wide-BW 3.6GHz Digital ΔΣ Fractional-N Frequency Synthesizer with a Noise-Shaping Time-to-Digital Converter and Quantization Noise Cancellation , 2008, 2008 IEEE International Solid-State Circuits Conference - Digest of Technical Papers.